1. The Field of the Invention
The present invention relates to drilling systems and to down-hole vibratory units in particular.
2. The Relevant Technology
Core drilling allows samples of subterranean materials from various depths to be obtained for many purposes. For example, drilling a core sample and testing the retrieved core helps determine what materials are present or are likely to be present in a given formation. For instance, a retrieved core sample can indicate the presence of petroleum, precious metals, and other desirable materials. In some cases, core samples can be used to determine the geological timeline of materials and events. Accordingly, core samples can be used to determine the desirability of further exploration in a given area.
Although there are several ways to collect core samples, core-barrel systems are often used for core sample retrieval. Core-barrel systems include an outer tube with a coring drill bit secured to one end. The opposite end of the outer tube is often attached to a drill string that extends vertically to a drill head that is often located above the surface of the earth. The core-barrel systems also often include an inner tube located within the outer tube. As the drill bit cuts formations in the earth, the inner tube can be filled with a core sample. Once a desired amount of a core sample has been cut, the inner tube and core sample can be brought up through the drill string and retrieved at the surface.
While such a configuration allows for the retrieval of core samples, the core sample can occasionally become jammed. For example, when using a core-barrel system to retrieve core samples in formations that contain unconsolidated or blocky ground, the core sample can jam or become lodged within the inner tube. This jamming can cause the weight of the drill string to be transferred substantially away from the outer tube to the core sample and the inner tube. This weight transfer can cause the core sample to fracture, which in turn can cause the slow or stop the core drilling operation entirely. Even if drilling continues, the head of the core sample in the bit can mill the formation and render that portion of the formation permanently unrecoverable. Thus, a core sample that is jammed in the inner tube can slow the drilling process and reduce the overall productivity of the drilling process.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein can be practiced